I am trying a design of mine that provides a two speed drive for the lathe that is changable while operating and also acts as an automatic transmission under load.
It has two ratios, high speed is about a 6 to 1 and low speed is about 50 to 1. It can be switched at any time while running or stopped by moving one lever. Also, if running in high speed and the machine bogs down instead of jamming it automatically kicks into low gear with much greater torque.
The secret to the operation is a one way clutch on the compound pulley of the low gear belt train. The lever merely applies or removes tension to the high speed direct drive belt. If the high speed belt is under tension the spindle turns faster than the one way clutch and the clutch is overrun. If tension is removed from the direct drive belt or the spindle slows because of load then the clutch begins to assume the load via the compound belt drive while the direct drive belt turns at low speed so it will not be burnt while slipping.
This is not a permanent feature. I decided to try it mainly for fun and because I need to finish other parts before working on the electronics. Eventually the drive will be either via VFD or if a DC motor then via servo feedback. It is looking like the DC motor will be sufficient especially in a servo configuration. In the meantime this drive will be a convenient method of operating the machine.